Polymeric or polymer based surfaces are often difficult to wet and bond because of low surface energy, incompatibility, chemical inertness, or the presence of contaminants and weak boundary layers. The lack of adequate adhesion at the substrate/adherent and/or reinforcement/matrix interfaces often results in poor material performance and limits the possible applications of the polymeric materials. Effective surface treatments are frequently required to overcome one or more of the abovementioned difficulties in order to achieve controlled or maximised composite performance and controlled level of adhesion with adhesives, coatings, etc.
In practical applications, solid polymeric material surfaces may also be required to exhibit a specific level or gradient of wettability by organic and/or inorganic liquids or vapours of these liquids. Depending on specific end-applications, the liquid phase or condensate may require to form a uniform film on the wettable solid's surface, or alternatively it may be required to bead-up on an unwettable liquid-repellent surface. With regard to the wetting capability by water-based media, the former material is defined as hydrophilic, and the later as hydrophobic. It is also possible that in some instances, an intermediate level of wettability is desirable.
Another important area of application of polymeric materials is in the biomedical field. To design a useful biomedical material, it is important to consider both bulk and surface properties of the material. Historically, selection of a biomedical material for a particular application has been based upon bulk property specifications. However, there is increasing recognition that a biomedical material must exhibit a specific surface chemical behaviour in order to minimise interfacial problems with host tissues and fluids. Thus, it is often required that the surface of biopolymer be chemically modified so that surface and interface behaviour could be controlled.
Various surface treatment processes have been developed to achieve different specific requirements. These include chemical oxidation with the use of oxidising agents; surface chemical grafting and various physical-chemical methods such as corona discharge; flame treatment; plasma treatment; and UV irradiation. Simple oxidative treatments by flame treatment, corona discharge, or chemical oxidation generally lead to a noticeable increase in surface hydrophilicity, and bonding ability as a result of the occurrence of oxygenated groups such as carboxyl, hydroxyl and carbonyl on the modified polymer surfaces. Such modified surface is, however, not stable and the chemistry and/or increased hydrophilicity is not permanent. This may be due to the partial removal low molecular weight oxidised material by a polar solvent or water from the oxidised surface. Alternatively, or in addition, it may be due to the reorientation of the surface functional groups which rotate inwardly into the bulk of the polymer during the storage or the use of such treated materials. Plasma treatment and/or plasma polymerisation is known to significantly improve bonding ability of the treated polymers or to achieve desired level of wettability as a result of selective incorporation of different types of chemical species onto the polymer surface through the use of an appropriate treatment gas or a monomer under controlled process conditions. Similarly to the oxidised surface, however, the plasma treated polymer surface is not stable in storage because of rotation and migration of the generated surface functional groups into the bulk of the material and the occurrence of post-chemical reactions within the modified surfaces. An additional drawback with plasma treatment or plasma polymerisation resides in the expensive process apparatus required and the high cost associated with the on-going operations and the difficulties experienced in carrying out the surface treatment continuously.
International Patent Application No. PCT SE89-00187 discloses a method of increasing the hydrophilicity of the polymer surface by a 3-steps process comprising: (1): producing carboxyl, carbonyl and hydroxyl groups on the polymer surface by an oxidation treatment process such as etching with oxidising acid solutions, corona discharge, flame and plasma treatment; (2) reacting the groups on the oxidised polymer surface with a compound belonging to the following groups A and B, wherein group A includes heterocyclic compounds having three or four ring atoms, such as oxiranes, thiiranes, aziridines, azetidinones, oxetanes, and group B includes carbodiimides (R--N.dbd.C.dbd.N--R') and isocyanates (R--N.dbd.C.dbd.O, or N.dbd.C.dbd.O--R--O.dbd.C.dbd.N). The reaction according to step (2) has to be carried out in aprotic organic solvents, such as ketones and ethers due to the fact that the compounds in groups A and B are not stable in aqueous solution, and (3) post-treating the polymer material previously treated according to step (2) with further application of compounds containing nucleophilic groups, such as alcohols, water, amines, carboxylic acids and hydroxycarboxylic acids which react with the modified surface either by opening aziridine rings, or react with the residual isocyanate groups.
Japanese Patent Publication No. Sho 56-16175 teaches that the poor bonding between an oxidised polyolefin and resorcinol or epoxy adhesive is due to the inability of the adhesive resin molecules to microscopically approach polar groups at an oxidised polymer surface. The method proposed to alleviate this problem involves treating the oxidised surface with a low viscosity solution of a low molecular weight compound whose chemical constituents are the same as or similar to those used for the cure of the two-component epoxy or resorcinol adhesives. These, in turn, affiliate with the polar groups of the oxidised polymer and subsequently act as a setting agent for the adhesive resin. The process described in the document is stated to be effective when the setting agent is not of the oxidative type. In the step of treating the oxidised surface of the polyolefin a 1 to 5% aqueous solution of a low molecular weight amine is applied which is dried on the surface and the surface is subsequently bonded using resorcinol or epoxy adhesive at about 80.degree. C. We have found that the amines, when applied by this method, act as a weak boundary layer having an adverse effect on adhesion.
It is an objective of the present invention to alleviate or overcome one or more difficulties related to the prior art. We have found that oxidation of the polymer surface and reaction of the oxidised surface with a multi-functional amine containing compound allows the surface to be permanently modified with selected inorganic and/or organic functional groups and molecular structures for specific purposes, such as adhesive bonding, coating, changing or controlling wettability, biocompatibility, and improving composite performance, etc.
The present invention provides a method of modifying at least part of the surface of a polymer including:
(i) oxidising the surface of a polymer substrate by any suitable oxidising means such as corona discharge, flame treatment, chemical oxidation, photo-chemical oxidation and non-depositing plasma treatments; PA1 (ii) exposing the oxidised polymer surface to at least one multi-functional amine containing organic compound and bonding the said multi-functional amine containing organic compound to the oxidised surface. When the multifunctional amine-containing organic compound is applied in a solution of concentration 0.5% by weight or more, the treated polymer surface is washed to remove excessive multi-functional amine containing organic compound. Preferably the surface is washed even when concentrates of less than 0.5% are used. PA1 E=Pn/lv.sub.1 PA1 E=Pn/lv.sub.2 PA1 t=treatment time for a single pass of treatment under the electrode PA1 d=electrode diameter PA1 E=discharge energy PA1 P=power energy PA1 n=number of cycles of treated substrate moving under the electrode PA1 l=length of treating electrode PA1 v.sub.1 =speed of treating table PA1 v.sub.2 =speed of conveyor tape (i.e. continuous treatment) PA1 AI: linear and carbon cyclic based multi-functional amine (at least diamine) compounds containing 2 to 60 carbon atoms, preferably 2 to 36 carbon atoms PA1 AII: polymer containing a multiplicity of amine functional groups such as polyamine compounds with molecular weight ranging from a few hundreds to a few millions PA1 BI: Perfluoroamines: e.g. perfluoroethylamine, perfluorotributylamine, etc PA1 BII: Amino alcohols/phenols: e.g. 2-amino ethanol, 6-amino-1-hexanol, 2-amino-2-methyl-propanol, 2-amino-2-ethyl-1,3-propanol, 4-aminophenol, etc; PA1 BIII: Amino polysaccharides: amino dextran, etc. PA1 BIV: Amino acids: e.g. 4-amino butyric acid, amino undecanoic acid, diamino butylic acid, 5-amino salicylic acid, etc: PA1 BV: Amino aldehydes/ketone: amino acetaldehyde (H.sub.2 NCH.sub.2 CHO), 1.3, diamino acetone, etc; PA1 BVI: Amino amides: amino acetamide (H.sub.2 NCH.sub.2 CONH.sub.2), poly(acrylic 6-acid 6-aminohexyl amide), amino butene thioamide, etc: PA1 BVII: Amino ethers: eg. 3-aminopropyl-n-butylether, 3-amino-1-propanol-vinylether, etc; PA1 BVIII: Amino esters: e. g. ethyl4-aminobutyrate, etc; PA1 BVIIII: Amino nitrites: e. g. .beta.-aminopropionitrile, methoxylaminoacetonitrile, diamino maleonitrile, etc; PA1 BX: Amino nitros: e. g. amino nitropyridine, etc; PA1 BXI: Amino thiols: e. g. 1-amino-2-methyl-2-propanethiol, etc; butylaminoethanethiol, etc; PA1 BXII: Amino phosphoric acids: amino propyl phosphoric acid, amino phosphonobutyric acid, aminobenzyl phosphoric acid, etc; PA1 BXIII: Amino sulfonic acids: 3-amino-i-propane sulfonic acid, amino benzene sulfonic acid, etc; PA1 BXIV: Amino halogens: amino chlorobenzyl alcohol, etc; PA1 BXV: Amino alkenes, amino alkynes: allyamine, diallyamine, triallyamine, etc. PA1 (i) when the untreated polymeric surface is hydrophobic providing a wettable surface and a water contact angle equal or less than 60.degree.; and PA1 (ii) when the untreated polymer surface is hydrophilic providing a non-wettable surface of water contact angle equal or greater than 90.degree.. PA1 Blood purification systems; Blood oxygenator for artificial lung, hemodialyzer and hemofilter for artificial kidney, filters for plasmapheresis or virus removal, adsorption column for detoxification, cell separator, immunoactivator; PA1 Prosthesis: blood access, vascular prosthesis, patch grafting, artificial cornea, artificial heart valve, blood pump for heart assist, contact lens, intraocular lens, bypass tube, catheter of hyperalimentation, hydrocephalus shunt, implants in plastic surgery, prosthesis and implants in dental surgery, wound dressing or covering; PA1 Disposable articles: Catheters, tubing, haemostatics, adhesives, syringe, suture
It is preferred that a single multi-functional amine containing compound be used however a mixture of two or more such compounds may be used if desired. The multi-functional amine containing compound may be used neat but is preferably used as solution of preferably 0.000001% to 10% by weight, or more preferably the concentration is less than 1% by weight (most preferably 0.01 to 1%).
In another preferred embodiment, the method of invention includes grafting a compound containing acidic group(s) onto the polymer surface through reaction with the multi-functional amine containing organic compound. The specific procedure used in this embodiment of the invention may include oxidation and reacting the oxidised polymer surface with the multi-functional amine containing compound in the presence of the compound containing acidic group(s) or alternatively reaction with the compound containing acidic group(s) can be carried out after the reaction between the oxidised polymer surface and the multi-functional amine containing compound has be completed. In this embodiment the amine/acidic group ratio used is greater than 1. This embodiment provides a modified polymer surface with a grafted double -layer molecular structure and a specific surface chemistry. A multi-layer may be obtained by repeating the above mentioned chemical treatment procedures to satisfy specific physical-chemical, rheological, and/or biocompatible requirements.
By the term "polymer", as used herein, we mean homo-polymers, co-polymers and/or their blends and alloys with other polymers and/or natural and synthetic rubbers, and polymer matrix composites, on their own, or alternatively as an integral and uppermost part of a multi-layer laminated sandwich comprising any materials e.g. polymers, metals or ceramics, or an organic coating on any type of substrate material. The term "polymer" means also a thermoset and/or a thermoplastic material.
The polymeric materials which can be surface modified by applying the present invention include, but not limited to, polyolefins such as low density polyethylene (LDPE), polypropylene (PP), high density polyethylene (HDPE), ultra high molecular weight polyethylene (UHMWPE), blends of polyolefins with other polymers or rubbers; polyethers, such as polyoxymethylene (Acetal); polyamides, such as poly(hexamethylene adipamide) (Nylon 66); halogenated polymers, such as polyvinylidenefluoride (PVDF), polytetra-fluoroethylene (PTFE), fluorinated ethylene-propylene copolymer (FEP), and polyvinyl chloride (PVC); aromatic polymers, such as polystyrene (PS); ketone polymers such as polyetheretherketone (PEEK); methacrylate polymers, such as polymethylmethacrylate (PMMA); polyesters, such as polyethylene terephthalate (PET); and copolymers, such as ABS, ethylene propylene diene mixture (EPDM). The polymer materials to be treated may be in the forms of flat sheets, films, complex shaped articles, particulate or powders, woven fabrics, and/or individual fibres. These can be solid polymeric mono-materials, laminated products or hybrid materials, or alternatively organic coatings on any type of the base substrate which can be non-metallic or metallic in nature.
Any suitable method may be used to oxidise at least part of the surface of the polymeric material. Such techniques include, but not limited to, corona discharge, flame treatment, non-depositing plasma treatment, chemical oxidation, UV irradiation and/or excimer laser treatment in the presence of an oxidising atmosphere such as, but not limited to: air, oxygen (O.sub.2), ozone (O.sub.3), carbon dioxide (CO.sub.2), Helium (He), Argon (Ar), and/or mixtures of these gases. However, for the present method the technique of an electrical discharge for instance corona discharge, flame treatment and/or chromic acid treatment are preferred.
Suitable corona discharge energies range from 0.1-5000 mJ/mm.sup.2 but more preferably 10-80 mJ/mm.sup.2. Corona discharge treatment may be carried out in the presence of the following atmospheres: air, oxygen (O.sub.2), ozone (O.sub.3), carbon dioxide (CO.sub.2), Helium (He), Argon (Ar), and/or mixtures of these gases. Suitable treatment times and discharge energies can be calculated using the following equations: EQU t=d/v.sub.1 (or v.sub.2)
where
or
When non-depositing plasma glow discharge treatment is used, the range of suitable energy is 5-5000 Watts for 0.1 seconds to 30 minutes, but more preferably 20-60 Watts for 1 to 60 seconds.
Alternatively, any known flame treatment may be used to initially oxidise at least part of the surface of the polymer or polymer based material. The range of suitable parameters for the flame treatment are as follows: the oxygen ratio (%) detectable after combustion from 0.5% to 5%, preferably from 0.8% to 2%; conveyor speed from 1 m/min to 800 m/min, preferably from 10 m/min to 100 m/min; treatment distance from 2 mm to 500 mm, preferably from 5 mm to 100 mm. Many gases are suitable for flame treatment. These include, but are not limited to: natural gases, pure combustible gases such as methane, ethane, propane, hydrogen, etc or a mixture of different combustible gases. The combustion mixture also includes air, any pure oxygen or oxygen containing gases.
Similarly, chemical oxidation of at least part of a polymer surface can be effected with any known, standard etching solutions, such as chromic acid, potassium chlorate-sulfuric acid mixtures, chlorate-perchloric acid mixtures, potassium permanganate-sulfuric acid mixtures, nitric acid, sulfuric acid, peroxodisulphate solution in water, chromium trioxide, or a dichromate solution in water, chromium trioxide dissolved in phosphoric acid and aqueous sulphuric acid, etc. More preferably, chromic acid treatment is used. The time taken to complete the treating process can vary between 5 seconds to 3 hours and the process temperature may vary from room temperature to 100.degree. C.
The current invention involves treatment of the surface of a polymeric substrate with a multi-functional amine containing organic compound. The multifunctional amine containing organic compound is a carbon, hydrogen and nitrogen containing compound which either has at least two amine groups or has one or more amine group(s) and at least one functional group other than the amine functional group(s). The compound may also contain one or more of the elements such as oxygen, sulphur, halogen and phosphorous in addition to carbon, hydrogen and nitrogen but generally will not contain silicon, titanium, zirconium or aluminium which are the basis of conventional coupling agents. Examples of multi-functional amine containing compounds having at least one amino group include compounds of groups A and B, wherein group A includes low and/or high molecular weight organic amines, that is compounds containing two or more amine functional groups. The amines can be primary, secondary, and/or tertiary amines, or a mixture of these three types of amines, however, primary and secondary amines are preferred due to their higher chemical reactivities in, comparison with the tertiary amines. Group B chemicals include multi-functional organic compounds in which at least one amine functional group and one or more non-amine functional groups are presented. The non-amine functional groups include, but are not limited to, the following functional groups and their mixtures: perfluorohydrocarbons, unsaturated hydrocarbons, hydroxyls/phenols, carboxyls, amides, ethers, aldehydes/ketones, nitriles, nitros, thiols, phosphoric acids, sulfonic acids, halogens. More specifically, the groups include, but are not limited to, any of the following chemical moieties:
eg. diamino propane, diamino butane, diamino pentane, diamino hexane, diamino octane, diamino decane, diamino nonane, dimino dodecane, hexamethylene diamine, pentaethylene hexamine, triamino pyrimidine, 1,2-diaminocyclohexane, etc.
eg. polyethylene imine, polyallylamine, polyvinylamine, etc.
All the compounds in class B (BI to BXV) may contain from 2 to 60 carbon atoms, preferably, from 2 to 36 carbon atoms in the case of low molecular weight compounds, and in the case where a polymeric compound is involved, the molecular weight of the compound may range from a few hundreds to a few millions.
The acidic group containing compound as used in the present invention in conjunction the multi-functional amine containing compound for achieving double or multi-layer surface grafting as specified previously in one of the preferred embodiment of the invention include compounds having at least one of the following acidic group or their hydrolysable salts such as, but not limited to, carboxylic/carboxylate, sulfonic/sulfonate and phosphoric/phosphonate groups. The compounds may also contain more than one type of acidic groups as well as other organic functional groups such as hydroxyl, amine, amide, ether, ester, ketone, aldehyde, halogen, etc, in their molecular structures. The acidic groups containing compounds can be small molecules with 2 to 60 carbon atoms, or macromolecules with molecular weight ranged from a few hundreds to a few millions. It is preferred that more than one acidic group be included in the molecular structure of the acidic groups containing compounds.
Preferably the acid group containing compound is selected from the group consisting of: polymers of monomers selected from the group consisting of acrylic acid, methacrylic acid, p-styrene carboxylic acid, 4-methacryloyloxyethyl trimellitate, vinyl sulphonic acid, p-styrene sulfonic acid, melaphosphonic acid; and copolymers including one or more thereof; and polysaccharide derivatives containing sulfonic/sulphonate and carboxylic/carboxylate groups.
Examples of the acidic groups containing compounds are as follows: carboxylic acid containing compounds (e.g. polyacrylic acid, polysaccharide derivatives containing carboxyl or carboxylate groups, polymethacrylic acid, poly(acrylic acid-co-maleic acid), poly(p-styrene carboxylic acid), poly(4-methacryloyloxyethyl trimellitate)); sulfonic acid containing compounds (e.g. polysaccharide derivatives containing sulfonic acid or sulfonate groups, poly(vinylsulfonic acid), poly(p-styrenesulfonic acid)); and/or phosphoric/phosphonic acid containing compounds (poly(metaphosphoric acid)). The concentration of the solution containing compounds having acidic groups is preferably 0.000001% to 10% by weight, or more preferably when it is 0.01% to less than 1% by weight. When the concentration is 0.5% by weight or more, said unreacted or excessive composition is washed from the treated polymer substrate prior to drying and further end-applications.
Both groups i.e. A and B of the multi-functional organic amine containing compounds and the acidic groups containing compounds may be applied from solution (dip, brush, spray), vapour or any type of mechanical dispersion of a pure chemical or their solutions and/or mixtures in any suitable solvent. According to the invention, any aqueous and/or organic solvent or a mixture of both may be used to prepare the reactive solutions so long as it does not attack the substrate and permits sufficient dissolution of the amine containing compounds claimed in this invention. Preferred solvents used for preparing the solution are water, and alcohols (ie. isopropyl alcohol, and ethanol).
We have found that the concentration of the multi-functional amine containing compound at the surface of the polymer substrate has a significant effect on the bond strength of the subsequently applied adhesive or coating. It might be expected that a higher concentration would provide a greater number of binding sites and hence greater strength as believed in the prior art. The reality is that the reverse is the case in many circumstances. Our experience as outlined in the examples of this patent clearly shows that the application of the grafting chemicals at a concentration of 1% by weight or more onto polymer surfaces without subsequent rinsing results in the formation of a weak boundary layer on the treated polymer surface due to the presence of loosely attached excessive molecules which are not chemically grafted onto the polymer surface. This consequently leads to the observed reduction of the bond strength and subsequent premature product failure upon exposure for instance to a humid atmosphere or immersion in a liquid such as water or other type of liquid. Accordingly it is preferred in our invention that the multi-functional organic amine containing compound is either (a) applied at a concentration in the range of from 0.000001% to less than 1% by weight preferably no more than 0.5% by weight (most preferably no more than 0.25%) or (b) that the multi-functional organic compound is allowed to react at the surface of the polymeric substrate and the excess is then removed by washing the surface of the polymeric substrate with water or a suitable solvent or a combination of both using either a single step or a multi-steps rinsing procedure. Most preferably both steps (a) and (b) are used, that is a dilute solution is used for the application of the multi-functional amine containing compound and the treated substrate is rinsed prior to drying and the subsequent end-applications.
The amine containing compound may be applied for any suitable time period from 0.0001 seconds to 24 hours at any suitable temperature from room temperature up to, and above the boiling point of these compounds. Preferably, the compounds are applied for 0.01 to 30 seconds at 20 to 100.degree. C.
For a given application, one or more multi-functional organic amine containing compound may be chosen in which the functional groups grafted onto the polymer surface have controlled or maximised reactivity at the interface. For example, if the substrate to be modified is to be bonded to a cyanoacrylate adhesive, a multi-functional organic amine would be selected in order to equip the polymer surface with the nucleophilic free amine groups which then initiate the cure and react with the adhesive during bonding and curing of the adhesive. XPS (X-ray Photoelectron Spectroscopy) analysis on HDPE treated by corona discharge oxidation followed by application of a multi-functional amine confirms that the amine compound was irreversibly grafted onto the oxidised polymer surface, and that 60% of the amine groups on the surface remain free for participating in further reaction(s).
It was also found that it is advantageous if during the treatment of the polymeric substrate with the multi-functional organic amine containing compound a suitable static and/or high frequency alternating physical field is simultaneously applied to the organic amine containing compound and/or to the substrate. For example, any one of the following fields may be used: ultrasonic, microwave, radio-frequency, heat energy or a combination thereof. Preferably an ultrasonic field and/or microwave is used.
According to the invention, optional organic functional groups become attached to a polymeric substrate surface by dipping the oxidised substrate into a composition containing the amine(s) with the simultaneous application of ultrasonic energy to the solution. The advantages provided by simultaneous application of ultrasonic field and/or microwave during the step (ii) of the treatment is to accelerate and promote the attachment of the selected chemical compound onto the polymer surface in order to obtain a modified surface with stabilised and improved physical and chemical properties. Further, the simultaneous application of an ultrasonic energy during the treatment is also possible to improve the orientation of the adsorbed molecules.
The preferred frequency range of ultrasonic energy field ranges between 1 to 500 kHz, more preferably between 10 to 50 kHz.
Preferably when used microwave energy is applied in the range of from 1 GHz to 300 GHz.
The present invention generally may be used to: 1) control or enhance the bonding ability of the polymeric materials to other materials including, but not limited to adhesives, sealants, coatings and any other reactive and/or non-reactive organic, inorganic or metallic materials, or mixtures thereof; 2) control surface energies and/or wettability therewith render hydrophobic polymeric materials hydrophilic or vice-versa; (3) improve composite performance through the surfaces of the polymer or polymer-based reinforcing materials being chemically modified according to the present invention in order to achieve controlled or maximised adhesion and rheological properties at the reinforcement (fibre or filler)/matrix interfaces; (4) improve biocompatibility of polymeric materials for various bio-medically related applications.
Following the treatment of a polymer or polymer-based material by the method of the invention the treated surface may be adhesively bonded to another substrate or coated.
When adhesively bonded to another substrate any suitable adhesive may be applied to the treated surface and then the other substrate is brought into contact with the adhesive. Suitable adhesives include, for example, cyanoacrylates, structural acrylic adhesives, polyurethane adhesives, silicone adhesives, sealants, unsaturated polyester adhesives, contact adhesives, or thermoplastic adhesives. Examples of particular suitable adhesives include, but are not limited to Cyanoacrylates Loctite 406, Loctite 454, acrylic Permabond F241, polyurethane Tyrite 7520 A/B. Preferably the adhesive will be cured at a temperature lower than 70.degree. C.
Alternatively, any suitable contact adhesive such as, but not limited to, self adhesive tape may be applied to the treated surface and then the other substrate may be brought into contact with the tape.
Preferably the method of the invention involves application of a coating composition to the treated polymeric substrate. The coating composition may be a metallic or a solid based paint, lacquer, varnish, enamel, water-emulsion, non-aqueous dispersion (organosol), plastisol or powder coating, radiation curable coating, sputter coating or the like.
When the treated substrate is printed with an ink, any suitable ink may be used.
Similarly, when the treated substrate is coated with a metallic material, any suitable metallic material may be used. Also, any coatings, based on aqueous and/or organic carrier and containing magnetic particles such as used in voice and/or image recording may be applied onto the substrate treated in accordance wish our invention.
The examples, by no means exhaustive, of technologically/biologically important areas that the polymer surfaces modified by the present method of invention can be applied to achieve controlled level of hydrophilicity or hydrophobicity are as follows:
Controlled evaporation/heat transfer:
Controlled/optimised solid's wettability provides the means for an increase or decrease of cooling liquid's evaporation rate, resulting in an optimised heat transfer through the heat exchanger's surface;
Printing:
Controlled/increased wettability of printing inks, coatings and other fluids on papers, polymers or metals, and controlled spreading of the printing substance on transfer platens and/or rolls;
Release coatings:
Controlled/minimised adhesion of any required substance (eg. water, oil, adhesive, paint, blood cells) on the release/anti-stick material surface;
Textiles:
Controlled/maximised spreading rate of fibre finishes, dyes, inks etc, or alternatively water, oil or soil/dirt repellency;
Decorative coatings:
Controlled/maximised spreading rate and adhesion of organic/inorganic/metallic or hybrid coatings applied onto the solid material's surface;
Surface cleanliness, colour uniformness and/or self-cleaning capability/enhancement:
Controlled/maximised spreading rate of liquids or vapours and/or good liquid film retention capability on the product surface finish.
The invention allows the wettability of polymer surfaces to be controlled by using an appropriate multifunctional amine-containing organic compound and optionally also the acid group containing compound. For example
This invention is particularly useful in modifying the hydrophilicity of polymer coated metal products. Hydrophobic polymers are commonly used as surface coatings to protect metal surfaces from tarnishing or corroding and for providing an attractive finish. Such coated metal products are widely used in the building and automotive industries. The hydrophobic nature of the polymer is particularly useful in these applications as it provides an effective moisture barrier. Notwithstanding this advantage, however, hydrophobicity of the surface detracts from the asthetics of the surface coating. When placed on the hydrophobic surface water forms beads which dry to form unsightly marks. The effect of the dried water beads is particularly detrimental in the presence of dust, dirt or salts.
The present invention allows the hydrophobic polymer to be applied as a coating to the metal to thereby provide the advantageous moisture barrier and the surface to be subsequently modified to improve its aesthetics without detracting from the protective function of the polymer coating. The invention also has the advantage that it allows the aesthetics of the surface to be improved without the need to change the current coating processes of the polymer or metal substrate used. The improvement in appearance is effected by treating the coated metal product by the means of the present invention.
In this embodiment of the invention the coating may be polyester, polyvinylidiene fluoride or any other polymer referred to above and the metal may be steel, aluminium or other metal or alloy. The well known COLOURBOND (trade mark John Lysaght Australia Pty. Ltd) products may be treated according to the process of this invention.
It is generally established that the contact angle of water on a wettable polymer surface should be lower than 60.degree. and preferably is below 45.degree. C. This is not easy to achieve on a number of substrate surfaces with conventional surface oxidation methods such as corona discharge, flame treatment and even non-depositing plasma treatments. Also the hydrophilicity created by these methods is not stable with time as mentioned earlier.
Therefore, the combination of a simple oxidation method and post-chemical grafting either by a 2-steps or a 3-steps process as specified in the present invention will provide suitable, stable and low cost hydrophilic surfaces to meet variable requirements,
Subsequent to the treatment of a polymer or polymer-based material by the method of the current invention the treated surface may be used for the various biomedical applications. Medical products made by use of modified polymeric materials include, but not limited to, the following applications:
Medical treatment
Drug delivery systems:
Transmucosa systems for glaucoma or contraceptive; transdermal systems for nausea, stenocardic, hypertension etc; polymer conjugate for antimalignancy; lipid microspheres for circular disorder and infectious disease; microcapsules and lipid microspheres in targeting
Clinical laboratory tests:
Dry reagent chemistry, immobilization of proteins, immobilized enzyme for biosensor, microspheres in immunoassay and measurement of biological activity of cells, nucleic acid hybridization assay, non-fouling surfaces and anti-bacteria attachment.
The invention will now be described in greater detail in conjunction with specific examples. It will be appreciated that the examples are provided for the purposes of illustrating the invention and that they in no way should be seen as limiting the scope of the above description.
In the examples, the surface of a range of substrates is treated by various methods and submitted to different end-applications.
After adhesive bonding, the specimens were allowed to cure for 72 hours prior to mechanical testing using single lap-shear test with an overlap of 3 mm. The test is carried out on an Instron mechanical tester at room temperature and at a cross-head speed of 10 mm/min.
In the case of coated specimens, an aluminium dolly is adhesively bonded to the cured coating film, and is subsequently pulled out under tensile stress in order to determine the strength of adhesion between the coating and the substrate.
The air/water contact angle measurements are chosen to provide an indication of the hydrophilicity of polymer surfaces before and after surface modifications. The contact angle measurements were carried out in ambient condition (20.+-.2.degree. C., relative humidity=50.+-.5%) using a Rame-Hart contact angle goniometer model 100-00. The air/water contact angle reading was taken immediately after the deposition of the droplet on the surface.
In the case of wettability measurements, experiments were carried out by counting the time required for a continuous water film to dry out from a polymer surface in the air. Each measurement was repeated three times consecutively. Bearing in mind that it is difficult to obtain absolute values from this type of measurements, it is probably more appropriate to classify the results in terms of "Good", "Moderate", "Poor", and "Very poor". "Good" means the formation of a complete water film on the polymer surface and a slow evaporation of water from such surface. More specifically, the estimated time during which the water film breaks on the edge of the specimen should be more than 15 to 30 seconds and the time required for drying out water from the centre of the specimen is more than 2 minutes. "Moderate" indicates that the water film breaks quickly on the edge of the specimen and that the drying time of water from the surface will be between 0.5 to 2 minutes. When a continuous water film can still be formed on the surface but it breaks quickly, then the surface is characterised as having "Poor" surface wettability. Finally, a surface failing to be covered by a continuous water film is identified as having "Very poor" surface wettability.